This invention relates to a mechanical disc brake and more particularly, to a mechanical disc brake which comprises a self-clearance adjusting mechanism having force conversion means adapted to convert a rotational input into a linear output.
A mechanical disc brake of the above type is disclosed in Japanese patent application No. 17,797, for example. However, in the above type disc brake, a lever return spring abuts at one end against one leg of the caliper and at the other end directly against the outer end of a nut through a stop ring, and the inner end of the nut engages a linear output generation member. Therefore, rotational force imparted to a lever is required to be greater than drag on rotation (Tn) generated between the nut and linear output generation member and between the return spring and stop ring, respectively. Furthermore, when the disc brake is released, drag on rotation (Tr) offered by the friction ring required to restrain the rotation of the nut should have a value greater than the value of Tn as a matter of course. On the other hand, when the brake clearance is to be adjusted, although the ratchet pawls of the leaf spring rotate the nut, the rotational force of these pawls is required to be sufficient to overcome the sum of the drag on rotation by the return spring and the drag on rotation by the friction ring, and as a result a grave problem arises as to how the enhance the durability of the pawls.